Added another version of bgets() which doesn't die on too long lines and

Added another version of bgets() which doesn't die on too long lines and
reports an error instead.

I wrote it originally for new http.c, but the required http.c changes were
going to be too extensive, so I postponed the changes and this function
is currently unused, but probably worth saving for the future.

Also optimized the existing bgets functions a bit.